The majestic greater sandhill crane, which normally makes a first appearance in area skies and marshes in mid- to late September, has returned unusually early to the Central Valley.

The early return has crane experts and birders contending that wildfires and drought are reasons for the migration change.

To date about 40 greater sandhill cranes, which are listed as a threatened species, have been roosting on Staten Island in the Delta.

The birds were spotted by farmer and birder Sally Shanks as early as Aug. 23. "In 25 years I've never ever seen them here before September," she said.

Shanks managed Staten Island with her husband in the 1980s and 1990s, and has been an advocate for the cranes. She contends that no one on the island – which is now run by the Nature Conservancy – was prepared for their early arrival, which may have been prompted by fires in Oregon.

"On Staten Island they provide early water for birds by flooding harvested wheat ground," said Shanks. "Of course, it is so early they were not ready yet, so birds are looking for puddles to stand in at night for their roost."

The birds started arriving more than two months ahead of the 2012 Sandhill Crane Festival. That two-day festival, based in Lodi, kicks off this year on Nov. 2.

Two sandhill species winter in the Central Valley: the greater sandhill and its smaller cousin, the lesser sandhill crane. The lesser migrates farther – from Siberian and Alaskan breeding grounds. The greater sandhill crane spends spring and summer months in southern Oregon, as well as the far Northern California counties of Modoc and Lassen.

"It's too early for them to be here," said Gary Ivey, western crane conservation manager for the International Crane Foundation.

The cranes make good use of corn and rice fields in the Sacramento Valley, as well as marshlands. They use wetlands for nighttime roosting as protection from coyotes and other predators.

Like Shanks, Ivey believes wildfires may be a reason for the early return.

The fire issue is no small matter this year. So far, 2012 is on pace to be one of the worst years in recent history for Western state wildfires.

According to the National Interagency Fire Center, 647 wildfires have burned more than a million acres in Oregon. The state's largest fire in more than a century took place in the southeastern part of the state, burning more than 800 square miles.

Drought also may have influenced the cranes to leave early.

"Their return may be related to drought conditions," Ivey said. "Overall, when food has been tougher to find further north the cranes have moved down."

Summer breeding grounds of the greater sandhill crane are in counties that have been designated drought disaster areas this year by the U.S. Department of Agriculture.

Ivey said he believes population increases may be another reason for the early appearance, and may also be causing some of the extremely territorial birds to move farther south.

If that is the case, it may signal a return of the cranes to former wintering grounds. Ivey, who grew up in Ceres, south of Modesto, remembers seeing the cranes there when he was growing up.

"There are no birds there now. They have vineyards," he said.

Vineyards are an example of one of the biggest threats to sandhill cranes: habitat change.

In the Sacramento Valley, those changes come from two factors. One is the threat of development, with the city of Elk Grove moving south into crane wintering grounds. The other is farmers forgoing grain crops such as wheat for row crops, such as grapes, olives or blueberries, said Ivey.

When row crops appear, cranes lose marshlands or the opportunity to use fields flooded by farmers.

"There are areas in the Delta that the cranes had been using in the 1980s for wintering grounds that are now vineyards," said Ivey. "We've probably lost at least a third to half of the cranes' wintering options because vineyards have come in."

And what about the lesser sandhill crane? They usually arrive later than the greater sandhill cranes.

Lesser sandhills have yet to migrate to the Central Valley along the Pacific Flyway, said Nina Faust, with Kachemak Cranewatch of Homer, Alaska.

The lesser sandhills have never left their traditional summering grounds in Homer earlier than Sept. 5, she said.

"Nothing unusual is going on this year with the lesser cranes," Faust said. "We have cranes gathering here at the same time they did last year, except this year maybe there are a little bit more of them."